Lubricating composition



United States Patent fiice 3,248,327 Patented Apr. 26, 1966 3,248,327 LUBRICATING COMPOSITION Arthur C. Whitaker, Pittsburgh, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Oct. 2, 1963, Ser. No. 313,179 Claims. (Cl. 252-522) This invention relates to an improved lubricating composition -and more particularly to a mineral lubricating oil composition having a reduced coking tendency.

The current trend in designing more efiicient and more economical automotive and aircraft engines has accentuated the need for lubricants which will effectively lubricate bearings operating under severe conditions, particularly under high temperature conditions. While considerable progress has been made in recent years in producing improved lubricants, some difliculty has been encountered in producing a lubricant which will effectively lubricate bearings operating at high temperatures for prolonged periods of time.

For many years, highly refined parafiinic oils have been used as base oils in forming lubricating compositions. By the term highly refined paraffinic oil I mean a petroleum lubricating oil which has been refined by one of the more drastic refining methods known in the art, for example, by conventional solvent extraction and aluminum chloride refining adapted to remove allor substantially all of the unsaturated and aromatic constituents of the oil. Aluminum chloride refined or solvent extracted paraifinic oils, such as the Pennsylvania oils, have provided excellent base oils for many lubricating compositions. Likewise, drastically refined Mid-Continent and Gulf Coastal oils have been widely used as base oils in forming lubricants.

In addition to these refining methods, lubricating oils of high quality have been obtained by hydrogenating various charge stocks derived from Pennsylvania, Mid-Continent, West Coast, Middle-East crudes, etc. It has been known, for example, that improved lubricating properties can be obtained when the lubricating oil stocks are treated I with hydrogen. Treating some lubricating oil stocks with hydrogen, for example, has resulted in obtaining stocks for making excellent multigrade lubricants, i.e., lubricantssuitable for use under a wide range of temperatures. Regardless of the treatment to which the various charge stocks are subjected, the mineral lubricating oil per se, which is obtained is not completely satisfactory for use under the severe conditions encountered in some of the current engines. Not all of the hydrogenated oils, for example, are sufficiently stable at an elevated temperature to meet the low coking requirements of the United States Air Force for certain aviation lubricants.

I have discovered that a lubricating composition having reduced coking tendencies can be obtained by incorporating in a mineral lubricating oil a small amount of a cyclic ether having the following structural formula:

where Y is selected from the group consisting of oxygen and Thus, the improved lubricating composition of my invention comprises a major amount of a mineral lubricating oil and a small amount, sufficient to reduce the coking tendencies of the oil, of a cyclic ether of the type designated by the above structural formula.

The R radicals can be like or unlike substituents in cluding hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, =octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, phenyl, naphthyl benzyl, tolyl, cyclo pentyl and cyclohexyl radicals.

Cyclic ethers having structural formulae illustrated hereinabove include m-dioxane, tetrahydropyran and their substituted derivatives. The :alkyl substituted cyclic ethers are particularly advantageous for use in lubricating oils according to the invention. While the alkyl radicals can contain from 1 to 14 carbon atoms, I prefer to use the alkyl substituted cyclic ethers wherein the alkyl radicals contain from 1 to 4 carbon atoms. As indicated by the structural formula, the substituted cyclic ether can contain up to 10 alkyl substituents. However, I prefer to use those substituted cyclic ethers containing from 1 to 4 alkyl radicals, the remainder of the R substituents being hydrogen. Thus, a preferred embodiment of the invention comprises a lubricating oil containing an alkyl substituted cyclic ether having a structural formula as shown hereinabove wherein from 1 to 4 of the R substituents are alkyl radicals containing from 1 to 4 carbon atoms and the remainder of the R substituents hydrogen. The methyl substituted derivatives of m-dioxane are good anti coking agents when incorporated in a mineral lubricating oil. I have found that the methyl substituted derivatives of tetrahydropyran are especially effective in reducing the coking tendencies of the oil. Specific examples of the especially preferred methyl substituted derivatives of mdioxane and tetrahydropyran are as follows:

. S-methyl-tetrahydropyran and R is selected fromthe group consisting of hydrogen,

G-methyI-tetrahydropyran 2,2-dimethyl-tetrahydropyran 2,4-dimethy-1-tetrahydropyran 2,6-dimethyl-tetrahydropyran 2,2,4-trimethyl-tetrahydropyran 2,4,6-trimethyl-tetrahydropyran 2,2,4,4-tetramethyl-tetrahydropyran 2,2,4,6-tetramethyl-tetrahydropyran Other compounds within the above formula are as follows:

m-Dioxane Z-ethyl-m-dioxane 4,4-diethyl-m-dioxane 2,4,6-triethyl-m-dioxane 2,4,5 ,G-tetraethyl-m-dioxane 2-propyl-m-dioxane 4-n-butyl-m-dioxane 4-tert-butyl-m-di0xane S-pentyl-m-dioxane 6-hexyl-m-dioxane Z-heptyl-m-dioxane 4-isooctyl-m-dioxane 6-nonyl-m-dioxane Z-decyl-m-dioxane 4-undecyl-m-dioxane 6-do-decyl-m-dio'xane Z-tridecyl-rn-dioxane 4-tetradecyl-m-dioxane 2,6-di-tert-butyl-4-methyl-m-dioxane 4phenyl-mdioxane 4-naphthyl-m-dioxane 4-benzyl-m-dioxane 4-tolyl-m-dioxane 4-cyclopentyl-m-dioxane 4-cyclohexyl-m-dioxane Tetrahydropyran Z-ethyl-tetrahydropyran 2,4-diethyl-tetrahydropyran 2,4,6-triethyl-tetrahydropyran 2,4,4,6-tetraethyl-tetrahydropyran 2-propyl-tetrahydropyran 3-n-butyl-tetrahydropyran 4-tert-butyl-tetrahydropyran S-pentyl-tetrahydropyran 6-hexyl-tetrahydropyran 2-heptyl-tetrahydropyran 4-isooctyl-tetrahydropyran 6-nonyl-tetrahydropyran Z-decyl-tetrahydropyran 4-undecyl-tetrahydropyran 2-dodecyl-tetrahydropyran 2-tridecyl-tetrahydropyran 4-tetradecyl-tetrahydropyran 2,6-di-tert-butyl-4-methyl-tetrahydropyran 2,6-di-tert-butyl-4,4-dimethyl-tetrahydropyran 4-phenyl-tetrahydropyran 4-naphthyl-tetrahydropyran 4-benzyl-tetrahydropyran 4-tolyl-tetrahydropyran 4-cyclopentyl-tetrahydropyran 4-cyclohexyl-tetrahydropyran The cyclic ethers employed according to the invention can be prepared according to known chemical procedures. Neither the compounds per se nor their method of preparation constitutes any portion of the invention.

The amount of the cyclic ether which I employ is an amount sufiicient to reduce the coking tendency of the oil. In most instances, this amount will be in the order of about 0.5 to-about 2 percent by weight based on the weight of the oil. In some instances, however, the amount will be in the order of about 0.5 to about percent by weight based on the weight of the oil.

The cyclic ether can be incorporated in the lubricating oil as such or it can be added to the oil in the form of a concentrated solution. The use of a concentrate is particularly advantageous where the amount of additive employed exceeds its solubility limit in the base oil. Any solvating agent which does not adversely affect the other desirable properties of the lubricant can be used.

The mineral oil in which the cyclic ether is incorporated can be any oil having a viscosity within the range of the common lubricating oils. The mineral oil, for example, can be either a refined or semi-refined parafiinic, naphthenic or asphalt base oil. A mineral oil which has been treated with hydrogen, because of its improved stability over the untreated oil, is particularly suitable as a lubricating oil base for preparing a lubricant to be used at an elevated temperature. For this reason, a preferred embodiment of the invention utilizes a mineral oil which has been treated with hydrogen whereby extensive hydrogenation of the olefinic and/ or aromatic constituents present in the charge stock has been effected. The hydrogen treating process may be either a hydrofinishing process or a hydrotreating process. The method by which a hydrogenated mineral lubricating oil is obtained is not a part of the present invention. The mineral oil content of the composition of the invention will vary depending upon the ultimate use for which the composition is intended. In general, however, the mineral oil content comprises about to about 99 percent by weight of the total composition. The particular mineral lubricating oil as well as the exact amount of such oil employed therefore depends upon the characteristics desired in the final composition.

In order to illustrate the reduced coking tendencies of lubricating compositions of the invention, a hydrofinished oil is compared with the same oil containing in one instance 2 percent by weight of 4,4-dimethyl-rndioxane and in another instance 2 percent by weight of 2,2,4-trimethyl tetrahydropyran. The test employed in the evaluation of the lubricating compositions is the Coker Dctergency Test.

The Coker Detergency Test is a modification of the Pratt and Whitney Test as described in the United States Air Force Military Specification MILL7 808A. In brief, the test comprises splashing the test oil against a heated aluminum panel for a given period of time and thereafter determining the amount of deposit formed on the panel. At the start of the test, 225 milliliters of test oil are placed in a stainless steel reservoir the oil being heated to a temperature of about 150 to 165 F. As the test progresses additional oil is added to maintain the initial volume of oil. During the test period, air is drawn over the oil at a rate of about 10 liters per hour. A cylindrical brush made of stainless steel wire is positioned over the oil reservoir so that a portion of the brush dips below the surface of the oil. The splasher brush rotates at a speed of about 1000 rpm. during the test period. By this means test oil is thrown from the oil reservoir to the underside of an aluminum panel positioned over the reservoir so that the oil after hitting the test panel can fall back into the reservoir. The test panel is maintained at a temperature of about 500 F. during the test period. The test may be conducted for various periods of time but for comparative purposes any series of tests are run for the same period of time. At the conclusion of the test, the air flow and heaters are turned off and the splasher is stopped. Excess oil is allowed to drain from the panel. The panel is then washed with petroleum ether to remove any free oil and thereafter allowed to dry. The dried panel is then weighed to determine the increase in weight. The increase is reported as deposit weight in milligrams.

The results obtained in the Coker Detergency Test are shown in Table I. The mineral oil employed was a hydrofinished oil having as typical characteristics an API gravity of 32.3; a viscosity of 148 SUS and 43.6 SUS at and 210 F., respectively; a viscosity index of a flash point of 425 F.; a fire point of 480 F.;

, a pour point of +5 F.; and a color ASTM Union of 1.

Table I Composition, Percent By Weight A B 0 Mineral oil 100 98 98 4,4-dimethyl-m-dioxane 2,2,4-trimethyl-tetrahydropyran 2 Inspection:

Coker Detergency Test, 8 hrs.Deposit;

Weight, mg a 36. 5

" Average of two reservoirs.

Table II Composition D F i G H I J Make-u percent by wt.:

Mineral Oil 95 m-D ioxane 4,4-diethyl-m-dioxane 4-tert-butyl-m-diman P 2,6-di-tert-butyl-4-methyl- Ill-d imzan P Tetrahydropyran 2,4,4,6-tetraethyl-tetrahydropyran A-tetradeeyl-tetrahydropyran 4-cyclohexyl-tetrahydropyran The lubricating oil composition of the invention can contain other addition agents normally added to lubricating oils for a specific purpose such as an oiliness and extreme pressure agent, an anti-oxidant, a corrosion inhibitor, a foam suppressant, a dye, a sludge inhibitor, a viscosity index improver, and the like. These agents can be separately added to the oil or they can be added in the form of a solution which contains one or more of such additives. If desired, the solution can also contain the cyclic ether.

While my invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

I claim:

1. A lubricating composition comprising a major amount of a mineral lubricating oil and a small amount, sufiicient to reduce the coking tendencies of the oil, of a cyclic ether having the following structural formula:

where Y is selected from the group consisting of oxygen and and R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl and cycloalkyl radicals each one of which contains not more than 14 carbon atoms.

2. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

where Y is selected from the group consisting of oxygen and and R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl and cyeloalkyl radicals each one of which contains not more than 14 carbon atoms.

3. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubrieating oil and about 0.5 to about 5' percent by weight of a cyclic ether having the following structural formula:

where R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl and cyeloalkyl radicals each one of which contains not more than 14 carbon atoms.

4. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

I- i R O R where from 1 to 4 of the R substituents are alkyl radicals containing from 1 to 4 carbon atoms and the remainder of the R substituents are hydrogen.

'5. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

R-C l R lN/R where from 1 to 4 of the R substituents are methyl radicals and the remainder of the R substituents are hydrogen. 6. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of 4,4-dimethyl-m-dioxane.

7. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating'oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

where R is selected from the group consisting of hydrogen, alkyl, aryl, aralkyl, alkaryl and cycloalkyl radicals each one of which contains not more than 14 carbon atoms.

8. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

where froml to 4 of the R substituents are alkyl radicals containing from 1 to 4 carbon atoms and the remainder of the R substituentsare hydrogen.

9. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral lubricating oil and about 0.5 to about 5 percent by weight of a cyclic ether having the following structural formula:

where from 1 to 4 of the R substituents are methyl radicals and the remainder of the R substituents are hydrogen.

10. A lubricating composition having a reduced coking tendency comprising a major amount of a mineral 1ubri-- eating oil and about 0.5 to about 5 percent by weight of 2,2,4-trirnethyl-tetrahydropyran.

10 DANIEL E. WYMAN, Primary Examiner. 

1. A LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF A MINERAL LUBRICATING OIL AND A SMALL AMOUNT, SUFFICIENT TO REDUCE TO COKING TENDENCIES OF THE OIL, OF A CYCLIC ETHER HAVING THE FOLLOWING STRUCTURAL FORMULA: 